Sheet feeder for copying machines

Abstract

A sheet feeder is adapted to feed sheets, received in a stack within a sheet cassette, one by one by a feed roller which rocks in response to a feed signal. The sheet feeder includes a detecting member for detecting the number of sheets left within the cassette, and means responsive to a signal from the detecting member for controlling the timing when the feed signal is produced. In this manner, an amount of flexure produced in the sheet being fed before it reaches resistor rollers is maintained constant.

What is claimed is: 
     
       1. A sheet feeder including a cassette having a bottom plate which has one end urged to move upward and adapted to receive a stack of sheets thereon, and a feed roller responsive to a feed signal to rock into its operative position where it contacts an uppermost one of the sheets in the stack within the cassette to feed the sheets, one by one, out of the cassette; characterized by: means for detecting the height of said stack of sheets and for generating an output signal as a function thereof; and   means responsive to said output signal for varying the instant at which the feed signal is produced as a function of the height of the sheets in the stack.   
     
     
       2. A sheet feeder according to claim 1 in which a plurality of the detecting means are provided and spaced apart in the direction of the depth of the cassette. 
     
     
       3. A sheet feeder according to claim 1 in which the detecting means comprises a light reflecting plate attached to said one end of the bottom plate, and a combination of light emitting and light receiving elements disposed to detect movement of the light reflecting plate. 
     
     
       4. A sheet feeder according to claim 3 in which the light reflecting plate is formed with a slot which is elongate in the vertical direction parallel to the direction of the movement of said one end of the bottom plate, a fastener member extending through the slot to be secured to said one end of the bottom plate, whereby the light reflecting plate is mounted on the bottom plate in a manner to permit a relative movement therebetween, the light reflecting plate carrying a weight to maintain it in an upright position. 
     
     
       5. A sheet feeder according to claim 1 in which the detecting means comprises a magnet attached to said one end of the bottom plate, and a magnetic detecting element disposed to detect a magnetic force from the magnet. 
     
     
       6. A sheet feeder according to claim 1 in which an arm bears against the lower side of the bottom plate to urge its one end upward and in which the detecting means comprises a variable resistor exhibiting a resistance which changes in accordance with the movement of the arm. 
     
     
       7. A sheet feeder according to claim 1 in which the detecting means comprises an arm which bears against the lower side of the bottom plate to urge its one end upward, a magnet disposed for displacement in response to an angular movement of the arm, and a magnetic detecting element disposed to detect a magnetic force from the magnet. 
     
     
       8. A sheet feeder according to claim 1 in which the detecting means comprises an arm which bears against the lower side of the bottom plate to urge its one end upward, a light reflecting plate disposed for displacement in response to an angular movement of the arm, and a combination of light emitting and light receiving elements disposed to detect movement of the light reflecting plate. 
     
     
       9. A sheet feeder according to claim 1 in which said control means comprises means for producing a first feed signal responsive to a feed initiate signal and for producing a second feed signal which is delayed by a given time interval with respect to the first feed signal, selection means for selecting one of the first and the second feed signals, and drive means responsive to the selected feed signal to initiate a sheet feed operation from the cassette. 
     
     
       10. A sheet feeder according to claim 9 in which said means for producing the first feed signal comprises a first monostable multivibrator responsive to a feed initiate signal, and said means for producing the second feed signal comprises a second monostable multivibrator responsive to an output signal from the first monostable multivibrator. 
     
     
       11. A sheet feeder according to claim 9 in which said selection means comprises a first AND gate receiving an output signal from a first monostable multivibrator which produces a first feed signal and a signal from the detecting means, a second AND gate receiving an output signal from a second monostable multivibrator which produces a second feed signal and the inversion of a signal from the detecting means, and an OR gate receiving output signals from the first and the second AND gate, and in which the drive means comprises a third monostable multivibrator receiving an output signal from the OR gate, and a driver circuit responsive to an output signal from the third monostable multivibrator for causing a rocking motion of the feed roller. 
     
     
       12. A sheet feeder according to claim 1 in which the control means comprises a first monostable multivibrator triggered by a feed initiate signal and having a reset time determined by an RC time constant circuit including a resistor, the resistance of which is formed by a variable resistor having a resistance which changes in accordance with a movement of an arm which bears against the bottom plate, a second monostable multivibrator responsive to an output signal from the first monostable multivibrator for producing a drive output signal, and a driver circuit responsive to the drive output signal for causing a rocking motion of the feed roller. 
     
     
       13. A sheet feeder according to claim 3 in which said combination of light emitting and light receiving elements is disposed on a copying machine in which the cassette is loaded. 
     
     
       14. A sheet feeder according to claim 4 in which a plurality of said combination of light emitting and light receiving elements are provided and spaced apart in the direction of the depth of the cassette. 
     
     
       15. A sheet feeder according to claim 14 in which two combinations of light emitting and light receiving elements are provided and spaced apart in the direction of the depth of the cassette such that neither, one or both of said combination of elements are disposed opposite said light reflecting plate at first, second and third positions of said one end of the bottom plate. 
     
     
       16. A sheet feeder according to claim 5 in which said magnetic detecting element is mounted on a machine in which the cassette is loaded. 
     
     
       17. A sheet feeder according to claim 7 in which said magnetic detecting element is mounted on a machine in which the cassette is loaded. 
     
     
       18. A sheet feeder according to claim 8 in which said combination of light emitting and light receiving elements is disposed on a machine in which the cassette is loaded. 
     
     
       19. A sheet feeder according to claim 1 in which said detecting means generate said output signal in such a manner that the higher the stack, the later the signal feed is generated. 
     
     
       20. A sheet feeder including a cassette having a bottom plate which has one end urged to move upward and adapted to receive a stack of sheets thereon, and a feed roller responsive to a feed signal to rock into its operative position where it contacts an uppermost one of the sheets of the stack within the cassette to feed the sheets, one by one, out of the cassette; characterized by: means for detecting the height of said stack of sheets left in the stack within the cassette, said detecting means comprising a light reflecting plate attached to said one end of the bottom plate and a combination of light emitting and light receiving elements disposed to detect movement of the light reflecting plate; and   means responsive to a signal from the detecting means to control the timing when the feed signal is produced.   
     
     
       21. A sheet feeder according to claim 20, in which said light reflecting plate is formed with a slot which is elongate in a vertical direction parallel to the direction of the movement of said one end of the bottom plate, a fastener member extending through said slot to be secured to said one end of said bottom plate, thereby said light reflecting plate is mounted on said bottom plate in a manner to permit a relative movement therebetween, said light reflecting plate carrying a weight to maintain it in an upright position. 
     
     
       22. A sheet feeder including a cassette having a bottom plate which has one end urged to move upward and adapted to receive a stack of sheets thereon, and a feed roller responsive to a feed signal to rock into its operative position where it contacts an uppermost one of the sheets in the stack within the cassette to feed the sheets, one by one, out of the cassette; characterized by: means for detecting the height of said stack of sheets left in the stack within the cassette;   means responsive to a signal from the detecting means to control the timing when the feed signal is produced;   an arm bearing against the lower side of the bottom plate to urge its one end upward, said detecting means comprising a variable resistor exhibiting a resistance which changes in accordance with the movement of said arm.   
     
     
       23. A sheet feeder including a cassette having a bottom plate which has one end urged to move upward and adapted to receive a stack of sheets thereon, and a feed roller responsive to a feed signal to rock into its operative position where it contacts an uppermost one of the sheets in the stack within the cassette to feed the sheets, one by one, out of the cassette; characterized by: means for detecting the height of said stack of sheets left in the stack within the cassette, said detecting means comprising an arm which bears against the lower side of the bottom plate to urge its one end upward, a magnet disposed for displacement in response to an angular movement of the arm, and a magnetic detecting element disposed to detect a magnetic force from the magnetic; and   means responsive to a signal from the detecting means to control the timing when the feed signal is produced.   
     
     
       24. A sheet feeder including a cassette having a bottom plate which has one end urged to move upward and adapted to receive a stack of sheets thereon, and a feed roller responsive to a feed signal to rock into its operative position where it contacts an uppermost one of the sheets in the stack within the cassette to feed the sheets, one by one, out of the cassette; characterized by: means for detecting the height of said stack of sheets left in the stack within the cassette, said detecting means comprising an arm which bears against the lower side of the bottom plate to urge its one end upward, a light reflecting plate disposed for displacement in response to an angular movement of the arm, and a combination of light emitting and light receiving elements disposed to detect a movement of the light reflecting plate; and   means responsive to a signal from the detecting means to control the timing when feed signal is produced.   
     
     
       25. A sheet feeder including a cassette having a bottom plate which has one end urged to move upward and adapted to receive a stack of sheets thereon, and a feed roller responsive to a feed signal to rock into its operative position where it contacts an uppermost one of the sheets in the stack within the cassette to feed the sheets, one by one, out of the cassette; characterized by: means for detecting the height of said stack of sheets left in the stack within the cassette; and   control means responsive to a signal from the detecting means to control the timing when the feed signal is produced, said control means comprising means for producing a first feed signal responsive to a feed initiate signal and for producing a second feed signal which is delayed by a given time interval with respect to the first feed signal, selection means for selecting one of the first and second feed signals, and drive means responsive to the selected feed signal to initiate a sheet feeding operation from the cassette.   
     
     
       26. A sheet feeder according to claim 25 in which said means for producing the first feed signal comprises a first monostable multivibrator responsive to a feed initiate signal, and said means for producing said second feed signal comprises a second monostable multivibrator responsive to an output signal from said first monostable multivibrator. 
     
     
       27. A sheet feeder according to claim 25 in which said selection means comprises a first AND gate receiving an output signal from a first monostable multivibrator which produces a first feed signal and a signal from the detecting means, a second AND gate receiving an output signal from a second monostable multivibrator which produces a second feed signal and the inversion of a signal from the detecting means, an OR gate receiving output signals from the first and the second AND gates and wherein the driving means comprises a third monostable multivibrator receiving an output signal from the OR gate, and a driver circuit responsive to an output signal from the third monostable multivibrator for causing a rocking motion of the feed roller. 
     
     
       28. A sheet feeder including a cassette having a bottom plate which has one end urged to move upward and adapted to receive a stack of sheets thereon, and a feed roller responsive to a feed signal to rock into its operative position where it contacts an uppermost one of the sheets in the stack within the cassette to feed the sheets, one by one, out of the cassette; characterized by: means for detecting the height of said stack of sheets left in the stack within the cassette; and   control means responsive to a signal from the detecting means to control the timing when the feed signal is produced, said control means comprising a first monostable multivibrator triggered by a feed initiate signal and having a reset time determined by an RC time constant circuit including a resistor, the resistance of which is formed by a variable resistor having a resistance which changes in accordance with the movement of an arm which bears against the bottom plate, a second monostable multivibrator responsive to an output signal from the first monostable multivibrator for producing a drive output signal, and a driver circuit responsive to the drive output signal for causing a rocking motion of the feeder roller.   
     
     
       29. A sheet feeder according to claim 20, in which said combination of light emitting and light receiving elements is disposed on a copying machine in which the cassette is located. 
     
     
       30. A sheet feeder according to claim 21, in which a plurality of said combination of light emitting and light receiving elements are provided and are spaced apart in the direction of the depth of the cassette. 
     
     
       31. A sheet feeder according to claim 30, in which two combinations of light emitting and light receiving elements are provided and are spaced apart in the direction of the depth of the cassette such that neither one or both of said combination elements are disposed opposite said light reflecting plate at first, second and third positions of said one end of the bottom plate. 
     
     
       32. A sheet feeder according to claim 23, in which said magnetic detecting element is mounted on a machine in which said cassette is located. 
     
     
       33. A sheet feeder according to claim 24, in which said combination of light emitting and light receiving elements is disposed on a machine in which said cassette is loaded.